Voltage divider with adjustable output characteristic



Dec. 18, 1956 1.. G. GITZENDANNER VOLTAGE DIVIDER WITH ADJUSTABLE OUTPUT CHARACTERISTIC Filed June 5, 1953 Inventor Louis 6- Gltzehdanner; by w 4. 7

His Attorney.

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United States Patent VOLTAGE DIVIDER WITH ADJUSTABLE OUTPUT CHARACTERISTIC Louis G. Gitzendanner, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 5, 1953, Serial No. 359,796

3 Claims. (Cl. 323-43.5)

My invention relates to voltage dividing circuits and has for one object the provision of a voltage divider whose incremental change in output voltage characteristic is adjustable to match many desired mathematical functions or curves.

Adjustable characteristic voltage dividers have heretofore generally taken the form of a plurality of resistance elements connected in series or in parallel and whose magnitude is adjusted or adjustable to correspond to the incremental change in output voltage desired. An output connection is made by suitable switching means to each resistance element in turn in order to produce a total output voltage whose characteristic simulates the desired function or curve. Since the voltages derived from each resistance element correspond only to discrete points upon a desired output voltage curve, interpolating potentiorneters are normally connected in parallel with such resistance elements and switching means are also included for connecting the output of each potentiometer in succession. In order to reduce the number of potentiometers employed, the same potentiometer is switched in parallel with each resistance element in succession, or two such potentiometers are switched between alternate resistance elements forming the entire voltage divider circuit.

The various switching means required in such conventional apparatus are, of necessity, of the snap acting variety, and elaborate mechanisms for insuring sychronism between the various switching means are incorporated in such devices in order to minimize the interruptions and discontinuities in the output voltage characteristic resulting from the various switching functions.

Accordingly, another important object of the invention is to provide an adjustable characteristic voltage divider in which the various resistance elements and their interpolating resistors are switched into the circuit without major interruption or discontinuity in the output voltage characteristic, and without the necessity of snap acting switches.

In general, my improved voltage divider circuit comprises a plurality of impedance elements of adjustable magnitude, an endless potentiometer having three spaced taps, and circuit means connecting each tap of the potentiometer to a different impedance element. By employing an endless potentiometer, there is no output switching required and thus no discontinuity in the output portion of the circuit. Moreover, by using a potentiometer hav ing three spaced taps, the potentiometer is divided into three impedance portions corresponding to three interpolating resistors, and the impedance of any one portion is not alfected by switching of the tap associated only with the other two portions. In this way, no discontinuity nor abrupt change in the output voltage characteristic appears when the various different impedance elements are switched into the circuit, and the switching can be accomplished with ordinary inexpensive slow-acting switches as well as by snap action type switches, and in any event the switching need not be accurately positioned with respect to the position of the interpolating potentiometer.

In one specific embodiment, switching means are provided for selectively and successively connecting each tap of the interpolating potentiometer to different impedance elements, while in an alternative embodiment switching means are provided for selectively energizing from a suitable voltage source different ones of the impedance elements connected to each potentiometer tap. A mechanical connection is made between such switching means and the movable tap of the potentiometer for correlating the movement of the movable tap to an interpolating resistor portion of the potentiometer between the fixed taps not being switched.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a circuit diagram of a voltage divider in accord with the invention in which switching means are provided for selective energization of the various resistance elements included therein; Fig. 2 is a circuit diagram of another voltage divider embodying the invention in which switching means are provided for making selective connection between the fixed taps of the endless potentiometer and the various resistance elements; and Fig. 3 is a plan view of a switching means suitable for use in connection with the device of Fig. 2.

Referring to Fig. 1, the invention is shown in one form as comprising a plurality of adjustable magnitude impedances shown as resistance elements 10 through 18. Resistance elements 10 through 18 may conveniently comprise potentiometers having adjustable taps 10a through 18a, as shown. Resistance elements 10 through 18 are arbitrarily arranged into three groups A, B, and C, preferably equal in number, and the adjustable taps of the resistance elements of each group are connected through common conductors 19, 20, and 21 to different ones of three preferably equally spaced fixed taps 22, 23 and 24 of an endless potentiometer 25. The potentiometer 25 comprises an endless or closed impedance, preferably circular, and the taps 22, 23, and 24 divide endless potentiometer 25 into three preferably equ-al resistance portions 26, 27, and 28 which function as interpolating resistors as will be explained hereinafter. Potentiometer 25 is also provided with a movable tap 29 which functions as the output connection for the voltage divider circuit. The impedance of each of the resistance portions 26, 27, and 28 is preferably made much larger than the impedance of any resistance element 10 through 18. Although potentiometer 25 is shown in diagrammatic form, it will be immediately recognized as a circular potentiometer of the type used in three wire direct-current selsyn systems, differing only to the extent that a single movable tap 29 is used rather than two 180-degree displaced movable taps.

In order to control the voltage presented to fixed taps 22, 23, and 24, switching means 30 are provided for connecting only one resistance element of each group A, B, and C in voltage measuring circuit relation with input terminals 37, 37a and the fixed potentiometer taps 22, 23, and 24. Switching means 30 has two sets of contacts 10b through 18b and through 18c, and the resistance elements 10 through 18 are each connected between a pair of contacts designated by the same reference numeral, a resistance element from each group being connected in succession to consecutively positioned contacts of the switching means 30. A pair of movable contact arms 31 and 32 make simultaneous connection to at least two and preferably three adjacent contacts in each set of contacts and are mechanically ganged together for corresponding movement. A unidirectional or alternating voltage source, shown for purpose of illustration as battery 33, is connected between input terminals 37, 37a connected, in turn, to contact arms 31 and 32. In the position of switching means 30 shown in Fig. 1, voltage is supplied only to resistance elements of group A, 11 of group B, and 12 of group C. As contact arms 31 and 32 are rotated, the remaining resistance elements 13 through 18 are each consecutively energized in groups of three.

Contact arms 31 and 32 are also mechanically interconnected as indicated by dashed line 35 with a movable contact arm 36 carrying movable tap 29 of endless potentiometer 25. The rotational movement of potentiometer contact arm 3-6 is correlated by this mechanical connection to the rotational movement of the switching contact arms 31 and 32 such that adjustable tap 29 always makes contact at any instant to a potentiometer resistance portion 26, 27, or 28 which lies between the pair of adjacent fixed contacts 22, 23, or 2 to which a resistance element is not being switched. For example, movable tap 29 is mechanically arranged to make contact with potentiometer resistance portion 27 during the time that one resistance element 19 of group A is being switched by the movement of contact arms 31 and 32 out of circuit relation with fixed tap 22 and a different resistance element 13 of group A is being switched into circuit relation with fixed tap 22. in a similar manner movable tap 29 makes contact to potentiometer resistnce portion 28 when resistance elements of group B are being switched into and out of circuit relation with fixed tap 23; and makes contact with potentiometer resistance portion 26 while resistance elements of group C are being switched into and out of circuit relation with fixed tap 24.

In the operation of the voltage divider circuit of Fig. l the adjustable taps of each of the resistance elements 10 through 18 are adjusted in turn to provide between the adjustable taps and the grounded output terminal 38 an output voltage corresponding to the mathematical or electrical values at points corespondingly spaced upon the analogous function or curve to be matched. The voltages appearing at fixed taps 22, 23, and 24 of circular potentiometer 25 depend upon the positions of the adjustable taps of the energized resistance elements of each group A, B, and C. The resistance portions 26, 27, and 28 of output potentiometer 25 thus function as interpolating resistors to provide intermediate values of output voltage as a result of the movement of movable tap 29 between the fixed output voltage values subsisting at fixed taps 22, 23, and 24 and derived from the three active resistance elements among elements 10 through 18. The instantaneous voltage appearing between output terminals 38, 33a as contact arms 31, 3-2, and 36 are rotated linearly between the voltages derived at successive adjustable taps lllathrough 18a of the resistance elements 10 through 18 as a result of the interpolating action of circular potentiometer 25.

It will be appreciated that battery 33 may be replaced by any suitable unidirectional or alternating-polarity voltage source. If alternating voltage excitation is used and alternating current impedances such as tapped coils substituted for resistance elements 10 through 18, the voltage divider of Fig. 1 may then be employed to follow matherriatical functions which vary not only in magnitude but also in phase, and the endless potentiometer 25 provides straight line interpolation between two vector quantities.

Referring now to Fig. 2, a second embodiment of the invention is shown in which a single multitapped potentiometer 4i) replaces the individual parallel-connected resistance elements it) through 3 of the device of Fig. 1, and a switching means 41 is connected between adjustable taps 42 through 53 of this potentiometer 4t and the three fixed taps 22, 23, and 24 of interpolating circular potentiometer 25, rather than between the potentiometer 40 and the voltage source as illustrated in connection with the device of Fig. 1. It will be appreciated that potentiometer 40, in electrical effect, is the same as a plurality of individual tapped resistance elements of the voltage divider type all connected together in series to form the single multitapped potentiometer 40. The total impedance of potentiometer 40 is preferably considerably less than the impedance of any portion 26, 27, or 28 of circular potentiometer 25. The input voltage source, shown for purpose of illustration as battery 33, is connected to opposite ends of potentiometer 40. Adjustable taps 42 through 53 of potentiometer 40 are each connected to a different fixed contact 42:: through 5341 of switching means 41; the numeral assigned to each contact corresponding to that used to designate the adjustable tap connected thereto. One suitable construction of switching means 41 is shown in Fig. 3. Fiyed contacts 42:: through 53:! are secured in a circle to a supporting flat board or card 54. Three contact arms 55, 56, and 57 extend radially from a central hub and are insulated from one another by an insulating collar member 59 serving also to connect arms 55, 56, and 57 to hub 53. Fixed contacts 42a through 53a are preferably closely spaced and contact arms 55, 56, and 57 are arranged to switch between only one pair of adjacent contacts at any instant of time. In other words, at least two of the contact arms 55, 56, and 57 are making good electrical connection with contacts 42a through 53a at all times. even when one of the contact arms is breaking connection between one contact and making connection to an adjacent contact during the simultaneous rotation of the three contact arms. Other well known types of switching means may, of course, be susbtituted for the switch shown in connection with Fig. 3. For example, linearly slidable contacts arranged as diagrammatically indicated in Fig. 2 or cam operated type switches may alternatively be employed.

Contact arm 36 of circular potentiometer 25 is mechanically interconnected with hub 58 of switching means 41 and rotates together therewith. The position of circular potentiometer contact arm 36 is correlated to the instantaneous position of the contact arms 55, 56 and 57 of the switching means such that movable tap 29 of circular potentiometer 25 is always in contact with one of the three resistor portions of circular potentiometer 25 that is remote from the fixed tap to which an adjustable tap of impedance-controlling potentiometer 40 is being switched. For example, as shown in Fig. 2, movable contact 29 of circular potentiometer 25 is positioned in contact with resistor portion 28 between fixed contacts 22 and 24- which are electrically connected through switching means 41 toadjustable taps 42 and 43 of potentiometer 40 while the fixed tap 23 is being switched by contact arm 57 of switching means 41 out of contact with adjustable tap 52 and into contact with adjustable tap 44 of potentiometer 40. It will be appreciated that although the adjustable taps 42 through 53 are shown as being connected in decreasing impedance sequence to the resistive element of potentiometer 40, this type of sequence need not necessarily be maintained. For example, tap 44 might be connected above rather than below tap 43. In this way both positive and negative slopes of the total voltage characteristic appearing between output terminals 38 and 38a may be provided.

It will thus be seen that I have provided voltage divider circuits capable of having as a function of contact arm position any desired output voltage characteristic which represents and matches any desired mathematical function or curve. The impedance components involved in the impedance system of the device are relatively few in number and the interpolating resistors comprising resistance portions 26, 27, and 28 of circular potentiometer 25 may be switched between various predetermined voltage points upon the representative curve without the necessity of a snap acting switching means.

Moreover, the use of a circular potentiometer eliminates discontinuities in the output voltage characteristic result- Although I have described above particular embodiments of the invention, many modifications may be made, and it is to be understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A voltage dividing circuit comprising a plurality of impedance elements each having an adjustable tap, an endless circular potentiometer having three spaced fixed taps and a movable output tap, switching means for consecutively connecting each fixed tap to the adjustable taps of different impedance elements, and a mechanical connection between said switching means and said movable output tap for correlating their movement and maintaining said output tap throughout its movement always in contact with a portion of said potentiometer between the fixed taps not being switched.

2. A voltage dividing circuit comprising an impedance element having a plurality of adjustable taps, an end less potentiometer having at least three substantially equally spaced fixed taps and a movable output tap, switching means for making connection from each fixed tap to different adjustable taps of said impedance element, said switching means being constructed to maintain the connection to two fixed taps while switching the connection to the third fixed tap, and a mechanical connection between said switching means and the output tap of said potentiometer for correlating the switching of the connection to each fixed tap with a position of said output tap intermediate the two fixed taps not being switched.

3. A voltage dividing circuit comprising a plurality of resistance elements each having an adjustable tap, an endless potentiometer having three substantially equally spaced fixed taps and a movable output tap, each fixed tap being connected to the adjustable taps of different resistance elements, switching means for consecutively making electrical connection to the resistance elements connected to different fixed taps, said switching means being constructed to maintain connection to the resistance elements connected to two fixed taps while switching the connection to the resistance element connected to a third fixed tap, and a mechanical connection between said switching means and said potentiometer output tap for correlating the switching to each resistance element with a position of said output tap intermediate the two fixed taps not connected to the resistance element being switched.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,950 Langguth et al Mar. 16, 1943 2,662,147 Wilentchik Dec. 8, 1953 FOREIGN PATENTS 451,786 Great Britain Aug. 12, 1936 

